How to choose a fuse?

Dec 30,2019

1. Safety regulation certification: according to the safety regulation certification required by the whole machine, such as UL specification or IEC specification, select the safety regulation certification of fuse.

2. Structure and size: select the fuse size according to the space in the circuit design, such as length, diameter, lead-free, etc.

3. Rated voltage: must be greater than or equal to the actual application voltage, generally including 24V, 32V, 63v, 125V, 250V, etc.

4. Breaking capacity: it shall be greater than the maximum fault current in the circuit.

5. Rated current: please refer to the following items:

（1） The normal working current is 25 ℃

UL rated current of fuse ≥ normal working current / 0.75;

Rated current of IEC fuse ≥ normal working current / 0.9.

(2) Ambient temperature: the current carrying capacity test of fuse is carried out under the ambient temperature of 25 ℃. The higher the ambient temperature is, the shorter the life of the fuse and the lower the bearing capacity. Therefore, the influence of ambient temperature on current carrying capacity should be considered when choosing fuse.

(3) Pulse: the pulse will produce thermal cycle and mechanical fatigue, thus affecting the life of the fuse. In the design, under the premise of considering the pulse factor, the pulse I? T shall be less than the nominal melting heat I? T of the fuse.

Fuse class I? T > practice pulse I? T / PF

PF: pulse coefficient, according to the acceptable number of pulses.

6. test

The samples selected through the above steps need to be tested in the actual circuit, and then verify whether the selected fuse is suitable. This verification shall include tests under normal and fault conditions to ensure the protection effect of the selected fuse in the protected circuit.

Keywords:

Fuse selection comparison

Three types of temperature fuse

Fuse selection comparison

Three types of temperature fuse